I have a Nikon camera. I received a Tamron 16-300 mm f/3.5-6.3 lens and a AF-S Nikkor 50 mm f/1.8G for Christmas. Do I need both? How do they differ in picture taking?
They are very different lenses and will go nicely together in the same camera kit.
We have an enormous amount of information on both types of lenses already on this site, so I'll just give you some keywords to search for to get you started in your research:
In regards to the Tamron 16-300mm:
- Variable aperture
- Zoom lens
In regards to the Nikkor:
- Prime lens
- Wide aperture
- Normal lens
- Portrait Lens
Do I need both?
You may or may not need both, but they're both very handy lenses to have.
How do they differ in picture taking?
Obviously, one is a zoom with a very wide range (which is good!) and the other is a prime (i.e. the focal length is fixed) with a pretty large maximum aperture (also good!).
The zoom will be great for shooting a soccer game, for example, because you can quickly zoom in to get a shot of a player on the other side of the field, or you can zoom out for a shot where the ball is close to you. When set to 16mm, the lens will be a fairly wide wide-angle lens, meaning that images will show a lot of the scene in front of the camera. At 300mm, the lens is a fairly long telephoto lens, meaning that it'll capture a much narrower part of the overall scene, making far-away subjects look larger. The ability to adjust the focal length without changing lenses is a huge benefit for all sorts of photography.
The 50mm f/1.8, on the other hand, doesn't have that same flexibility, but it's a great walking-around lens because it's smaller and lighter, and probably also somewhat sharper than the zoom. It also offers a larger maximum aperture, which means that it'll work better in low-light situations (like indoors), and it also lets you take photos with narrower depth of field. That means that you can take a picture where your subject is in focus but the background is (intentionally) out of focus, like this one*:
So, your 50mm f/1.8 will give you some creative freedom that the zoom won't, and because that larger aperture lets in more light it'll also let you shoot at a faster shutter speed or at the same shutter speed in lower light than you can with the zoom.
There's more to a lens than just focal length, and having a zoom lens that covers 50mm doesn't mean that having a great 50mm prime isn't also useful.
It mainly depends on your shooting style. I would keep the 50 (it is a very nice prime with good light, lenses faster than that come at $1000s) and trade the ridiculous, dark zoom for one good zoom (Tamron 28-75 2.8 maybe?) or a few primes. If you're not a nature photographer you'll hardly use anything above 100mm (mind that you need a tripod for your looooong and slow zoom!). I have a 70-200 lens and it's my least used lens. Remember also that such big zooms have poor picture quality usually (unless they cost in 10000 range...).
But maybe you want to take photos of far objects, then sell your 50 mm buy a good tripod... You just won't get the "pro" blurry background look though with this zoom...
Each lens has an individual character and tends to be better for specific types of uses. And that character and use may change, depending on the size of the sensor you're using as well.
Assuming you're using a crop body, then the 16-300 is a very versatile superzoom walkaround lens that can cover a wide variety of subjects: from wide angle landscapes to short telephoto portraits, and supertelephoto subjects like wildlife (ignore the macro claims. It's not really a macro lens, it only gives ~1:3 magnification). It's relatively large for a lens, but not as inconvenient to lug about as a 18-55 and 55-300 duo, so it makes a great travel lens for those times you want to go light.
The drawback of the 16-300, however, is that to cover such a large zoom range, there are image quality compromises. It exhibits strong lateral chromatic aberration in the 200-300mm range, it's generally softer in the corners and around the edges, and at the wide end exhibits the "wave" or "mustache" distortion typical of superzooms. And that it has a "slow" maximum aperture of f/3.5 at the 16mm end of the range, and f/6.3 at the 300mm end of the range, which means you'll need more light, higher ISO settings, or longer shutter speeds to get good exposures. None of this is unexpected in any superzoom lens, btw. Super-picky shooters prefer zoom ranges that are 3x or less (i.e., the ratio of the long end to the short one. The 16-300's is about 6 times that: 300/16 => 18.75x). There's no such thing as a perfect lens. Just tradeoffs that work better for you.
The 50mm f/1.8 was the kit lens for film SLRs. It's a "prime" lens (i.e., has a fixed focal length) with a large maximum aperture. It's small and compact. A large "fast" (anything f/2.8 or larger is considered fast) maximum aperture means you can probably use the lens indoors without a flash or in lower light. And given that it's a prime, it can achieve better image quality with a simpler design than a zoom. Compared to your 16-300, it's probably smaller, cheaper, and sharper. It's suited for portrait and available light shooting.
The drawbacks of the 50/1.8 are that on a crop-body dSLR, the field of view, thanks to the crop factor, is going to make it act more like a short telephoto lens (great for portraits, not so good for walkaround or landscape shooting), and because the lens doesn't zoom, you have to move around more to compose your shot, and there may be situations where it will be unsuited to the subject (i.e., small spaces, across-the-table portraits, unable to leave your seat in a performance venue, etc.) where a zoom would be a better fit. A lens that might be better suited, if you wanted a fast prime for street or walkaround shooting is the AF-S 35mm f/1.8G.